1. Field of the Invention
The present invention is related to an improved dial test indicator holder designed for use with machine tools.
2. Description of the Prior Art
Dial test indicators are utilized in the machine tool industry for performing a variety of measurements where precise machine cutting, boring, milling and other machining operations are conducted. Dial test indicators are used to ascertain the concentricity of positioning of a work piece relative to a spindle center line, to align the edge of a work piece with the longitudinal or transverse movement of a machine table, and to check perpendicularity of spindle center lines relative to the surface of a table. Other types of dial test indicators are utilized in height gauges in order to ascertain the uniformity of height of a machine tool relative to a work piece as measured at different points on the work piece.
A dial test indicator is employed to considerable advantage when it is mounted in a holder that can be attached to the spindle or collet of a machine tool, such as a milling machine. The spindle or collet of such a machine tool is generally referred to in the industrial machining industry as a quill. A dial test indicator holder typically employs a quill clamp, which is a generally C-shaped clamp that is fastened to the quill in a plane perpendicular to the quill axis. A dial test indicator holder normally has an articulated arm that extends from the quill clamp toward a work piece and carries at its extremity, remote from the quill, a dial test indicator. Manual rotation of the quill will carry the dial test indicator holder and the dial test indicator in rotation about the quill axis. Deflection of the needle of the dial test indicator is observed to detect eccentricity of boring or milling, and variations in height of a surface of a work piece or variations in the alignment of the edge of a work piece. A dial test indicator holder of the type described has a significant advantage in that the necessary tests for precision in machining can be performed without removal of a working implement, such as a drill bit, milling bit or other tool, from the collet or spindle of a machine tool. This avoids errors in machining which would otherwise occur due to minute variations in positioning that inevitably arise when a tool bit is removed from and reinserted into a chuck, collet or bit holder. One conventional dial test indicator holder is depicted and described in U.S. Pat. No. 3,442,478 and is sold commercially as the Indicol holder.
The Indicol holder employs a quill clamp and articulated arms that extend from the quill clamp to carry the dial test indicator. One of the arms may be adjusted in length by virtue of a sliding connection with the other arm. Releasable fasteners allow the effective length to be adjusted up to a maximum length as dictated by the maximum effective length of the adjustable arm.
The Indicol holder, and other conventional dial test indicator holders, have several disadvantages. Specifically, the effective length to which the articulated structure may be lengthened is limited to the length of the adjustable arm. If the adjustable arm is excessively long, conventional holders may not be utilized in close quarters, as the excess reach of the adjustable arm beyond the connecting joint will often interfere with the structure of the machine tool and surrounding, immovable structures when the quill is rotated and when only a small effective length is required. Thus, it has been the practice to manufacture different sizes of test indicator holders to be utilized in different environments. Due to the highly precise nature of the measurements which must be achieved, however, the test indicator holders must be very accurately machined. Consequently, the purchase of several dial test indicator holders to afford different measurements represents a significant expense to a machine tool user.
Another disadvantage of conventional dial test indicator holders is that various of the component links of such holders lie in different, parallel planes which are located horizontally off center from a vertical plane passing radially through the axis of a quill to which the dial test indicator holder is connected. As a result, conventional dial test indicator holders tend to twist very slightly under the force of gravity. Even a very tiny twisting action in the dial test indicator holder can result in the manufacture of defective parts which fail to meet the precision tolerance standards required in many precision machining operations.
A further disadvantage of conventional dial test indicator holders is that they often exhibit excessive springiness which can lead to errors in measurements and hence errors in precision machining operations.
A further disadvantage of conventional dial test indicator holders is that they are essentially single holder devices. That is, a dial test indicator holder designed for coupling to a quill by means of a quill clamp can not be used as a height gauge to measure the distance of a machine tool from a work piece. Conversely, dial test indicator holders utilized in height gauges cannot be adapted for connection to the quill or spindle of a machine tool to assure concentricity.